904 early shifts

Just recently it seems my 904 tranny has started shifting from 1st to 2nd and also from 2nd to 3rd at very short intervals and really low rpm's. If I nail the gas it holds to the higher rpm's as expected with no slipping that I can feel. It's always when I'm putting around. If I am making a left or right hand turn sitting at a red light, It will be in third before I even get the wheels straightened out from the turn and maybe 15mph tops. Any ideas on what to look at and check? This tranny is unknown on mileage and use. I got it with a 318 two years ago and just changed the filter, added a deep pan, and a shift kit. My kickdown is adjusted properly and working.